Rajarshi also built a Ubiquity command (more on Ubiquity here) that functions reasonably well as an interface- though still not as well as a simple Web form- and without a simple Web form, the tool isn’t really available to a lot of potential users.

I responded to Rachel’s original request at Twitter by saying that I used to look for the most frequent Subject Headings by one command in the (expensive) STN-database. I had no idea that this could be done for free with a 3rd party MEDLINE/PubMed tool. And now there are several possibilities! Very useful when one wants to get a hint of which MeSH are most appropriate.

Coincidentally I found another 3rd party tool which does the job, and in my opinion, even better: PubMed PubReminer

It’s lay-out isn’t very user-friendly, but if I type the 3 PMID’s you gave, it shows several lists with the most frequently occurring words on top.
These are the lists (columns): Year, Author, Journal, (Text)Word, MeSH, Substance, Country.

What I like most is that it also includes Mesh and their subheadings. To find the combination can be very important for your search (and it is this possibility I missed most in the other tools.)
For instance, your 3 PubMed ID’s yield: Urinary Catheterization/instrumentation twice and Urinary Tract Infections/etiology once.